Bloomington

Project Overview:

The Nine Mile Creek Watershed District and the City of Bloomington are implementing a multi-stepped approach to improve the health of Normandale Lake—a shallow lake with a large, urban watershed. To date, projects include a lake drawdown (2018-2019), aluminum (alum) treatment (2019), herbicide treatments (2020-2026), and carp management.

About Normandale Lake

Image of a map of the Normandale Lake drainage area
Area of land that drains to Normandale Lake

Normandale Lake was created as part of a flood control project in the late 1970s by the District and City of Bloomington in an area of natural marsh land. A permit for the construction of the lake was issued by the Army Corps of Engineers, which limits some management options for Normandale Lake, such as aquatic vegetation harvesting and dredging on the western half of the lake. Normandale Lake is a shallow lake (three-foot average depth). This means aquatic plants naturally grow throughout the lake. A robust, native aquatic plant population is part of a healthy shallow lake.

Normandale Lake receives water from a drainage area of over 34 square miles, including water from six different cities. The water flows into the lake through Nine Mile Creek and stormwater pipes. Nutrients, such as phosphorus and nitrogen, from sources such as grass clippings, tree litter, lawn fertilizer, and sediment from paved surfaces and erosion travels with this water. This is called external nutrient loading. Internal loading is when phosphorus is released from lake bottom sediments. Excess nutrients can fuel algae growth in the lake.

Normandale Lake is not currently on the state’s impaired waters list but does frequently have phosphorus levels that exceed state standards (>60 µg/L). Historically, Normandale Lake has met the chlorophyll-a and Secchi disc depth standards for shallow lakes.

Project Goals

Improve the water quality and the ecological health of Normandale Lake by:

  • Controlling invasive curly-leaf pondweed
  • Improving the diversity of native plant species
  • Reducing phosphorous
  • Controlling the invasive carp population

Project Details:

The Normandale Lake Improvement Project has involved multiple lake management strategies to achieve project goals.

Lake Drawdown

Image of Normandale Lake during draw down project
Normandale Lake during drawdown (2018)

Curly-leaf pondweed is an invasive plant that out-competes native aquatic plant communities. The plant can also contribute to high phosphorous levels in a lake when it dies off and decays mid-summer. A drawdown is one way to control curly-leaf pondweed. Curly-leaf pondweed primarily reproduces through vegetative propagules called turions. The plant produces turions in late spring, the turions remain dormant in the sediment through the summer, and then germinate under cooler water conditions in the fall. A winter freeze of the lake sediment bed (while the lake is empty of water) can kill the turions, thus stopping the curly-leaf pondweed’s reproductive cycle.

Curly-leaf Pondweed Herbicide Treatment

Image of an herbicide boat on Normandale Lake
Herbicide treatment boat on Normandale Lake (2020)

The lake drawdown decreased the amount of curly-leaf pondweed in the lake. Follow-up herbicide treatments were planned as part of the project to manage any curly-leaf pondweed that remained following the drawdown. The District assesses the need for an herbicide treatment yearly, based on plant surveys. Current project plans include up to five years of treatment, after which the effectiveness and long-term sustainability of the curly-leaf pondweed management strategy will be re-evaluated. Partial lake herbicide treatments have occurred from 2020-2026.

Alum Treatment

Image of Alum Floc
Alum floc in Normandale Lake during alum application (May 8, 2019)

Aluminum sulfate treatments help control internal phosphorous loading in lakes, reducing the phosphorus available to fuel algae growth. The Normandale Lake alum treatment was conducted in 2019, after the lake refilled from the drawdown.

Carp Management

Carp are an invasive species of fish. They stir up lake bottom sediments while feeding which reduces water clarity and releases phosphorus. They also uproot aquatic vegetation, destroying habitat for waterfowl and aquatic communities.

Since 2020, the District has been working to manage carp population levels in Normandale Lake. Since 2020, over 7,500 carp have been removed from Normandale Lake.

Learn more about carp management at Normandale Lake by watching this YouTube video:

View video transcript
Okay, go. Today on Normandale Lake we are setting and raising some carp traps. One way of doing it in a shallow lake is either through seining, near shore seining, or box trap nets. So we’ve been having a program right now where we are putting out a couple, I think there’s three different box trap nets on the lake that we have volunteers bait with corn, cracked corn, and then we have pulls every now and again to try to remove as many as we can.

Last year we removed over 5,000 large carp in the lake. We’ve been partnering with the watershed district on work out here at Normandale Lake for the last few years. I tend to serve as the liaison and help coordinate if the watershed district calls and says, “Hey, can you line up some volunteers to help bait traps?” Well, carp pulling is part of a larger phased project for Normandale Lake. The City of Bloomington and Nine Mile Creek Watershed District have been very interested in trying to improve the overall water quality and ecological health of Normandale Lake. Watershed District undertook a study back in 2017 to look at the water quality and potential projects to improve it.

Carp management is one of those to try to help reduce the internal load or nutrient loads coming from the sediment. As the carp root up the sediment, and when they kick up that mouthful of mud or sediment on the bottom of the lake, it turns the mud into the water column, which makes it really murky. It also releases phosphorus, which in turn is essentially food for algae blooms which we’ve been seeing are a big problem around the metro area for sure. They’re also uprooting small plants that are in the lake, which are good for the lake because they are habitat for things like bluegill sunfish, which then are food for bass and pike, which are the fish that we all like to angle for and catch. And so they can have an effect on the environment that disrupts the bottom of the food chain of fish in our lakes that we think of as a healthy ecosystem.

The district has been undertaking a carp management analysis in the lake to determine how many carp we have and also to try to put antennas in them so they follow where they go so we can best find places to remove them. Carp have the ability to traverse through almost little or no water, so places that are swamps or little creeks, even if most the time they’re dry, and then eventually wash their way into lakes. And then once they’re in a lake chain, they can move sometimes freely between them. So we find out also where they’re moving and when, and if that information comes about where we can use that for management, then that’s another opportunity to keep their numbers down.

So the process with these baited box net traps: first we install them in places that we feel that they’re going to be appropriate, where number one, we’re seeing lots of carp sort of around the area. They don’t catch any non-target fish; they’re very targeted to common carp. And we train those fish over a number of days with this bait, and we keep replenishing it every day as they eat through it all. And that means that they’re learning that if I return to this spot every day, then I’ll get free food. And then we use that to our advantage to plan a time to come and raise the outer walls of the net, and if we do that quickly they don’t have enough time to be disturbed and leave the area where the net is around them. And then once we get them in the net, we pull a boat up to them, to the side of the short side of the net, and we corral them over to one end and we just roll whatever we’ve caught into the boat.

We have strict guidelines on what we can do with these carp once we remove them. We act under a Minnesota DNR research permit and we can either bury them, incinerate them, or donate them to the licensed commercial fishermen of the area. So we’ll have these traps running at least through the end of August and maybe into September too to see how we’re doing, and we’ll compare that to our population estimates on how effective we are at getting a chunk of the population out of the lake. It’s going to be a continual program until our analysis gets ourselves in a steady state. We’ll never remove all the carp, but we want to make sure we get to a place where we can readily manage it and they’re just not overtaking the lake.

Fisheries Management Resources:

Integrated Pest Management Plan for Common Carp in Normandale Lake_1/26/23

Project Monitoring

Image of graphic of monitoring activities in Normandale
The District is undertaking a comprehensive monitoring program to assess the effectiveness of management activities on Normandale Lake.

The District is implementing a comprehensive targeted monitoring program to assess the effectiveness of the Normandale Lake Project management activities as they are implemented. This will allow the District to evaluate the ongoing need for additional or repeat management activities. The District will conduct monitoring activities to measure water quality, particularly phosphorus, the health of the aquatic plant communities in Normandale Lake, and to measure the amount of curly-leaf pondweed in the lake.

Project Updates:

A partial lake herbicide treatment to control curly-leaf pondweed has completed in May 2026.

Project Timeline:

Questions?

Erica Sniegowski, District Administrator,  952-658-9024, esniegowski@ninemilecreek.org